Radial artery occlusion (RAO) can result from transradial catheterization. We compared the incidence of RAO with 2 heparin dosage regimens after transradial coronary angiography, and we evaluated the efficacy and safety of transient homolateral ulnar artery compression to achieve acute radial artery recanalization. Patients referred for coronary angiography were randomized to very-low-dose heparin (2,000 IU) or low-dose heparin (5,000 IU). On sheath removal, hemostasis was obtained using the TR band with a plethysmography-guided patent hemostasis technique. In the case of RAO as assessed by duplex ultrasonography 3 to 4 hours after hemostasis, immediate 1-hour ulnar artery compression was applied. Hematomas >15 cm(2) were also assessed. We randomized 465 patients, 222 in the 2,000-IU group and 243 in the 5,000-IU group. The baseline and procedural characteristics were comparable in both groups. The incidence of initial RAO was 5.9% in the 2,000-IU group and 2.9% in the 5,000-IU group (p = 0.17), with a compression time of 2.10 ± 0.78 hours and 2.25 ± 0.82 hours, respectively (p = 0.051). After ulnar artery compression, the final incidence of RAO was 4.1% in the 2,000-IU group and 0.8% in the 5,000-IU group (p = 0.03). The incidence of local hematoma was 2.3% and 3.7% in the 2,000- and 5,000-IU groups, respectively (p = 0.42). In conclusion, acute RAO after transradial catheterization can be recanalized by early 1-hour homolateral ulnar artery compression. This simple nonpharmacologic method was effective and safe in patients with very-low- and low-dose heparin. Nevertheless, the incidence of final RAO remained significantly lower after a higher anticoagulation level.